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From "Hung Tang" <>
Subject persistent connections: understanding socket programming in tomcat help
Date Wed, 02 Aug 2006 21:45:21 GMT

My requirement is to write a server that is capable of holding long
conversations with the client based on socket programming for Java.  I'm
using ServerSocket to create TCP sockets.  The problem I am running into is
that I am not able to do [read, write, read] sequence of operations reliably
on my socket.  Here is my [read, write, read] code:

1: int numBytesRead = socket.getInputStream().read(buffer);
2: System.out.println(numBytesRead);
3: socket.getOutputStream().write(new byte[] { 'a', 'b', 'c' });
4: socket.getOutputStream().flush();
5: numBytesRead = socket.getInputStream().read(buffer);
6: System.out.println(numBytesRead);

On line 5 in this code, the read operation is NOT blocking and will return
-1.  After some testing, I concluded that after flushing output [line 4],
the input stream will not block anymore.  However, if I comment out line 4,
the read operation will block again, and will continue to block on
subsequent attempts for read before any output flush.  What I want is to
implement persistent connections which enable me to read client's input,
respond, and repeat without closing the socket.  I believe this possible
with Tomcat but I can't figure out how Http11Processor implements it.

Can anyone give me any ideas as to WHY this is the behaviour to be expected
in my code?  Why is that a output flush causes my input stream to behave
unexpectedly? And how do I correctly implement read, write, read for support
persistent connections?  Surely this can be done right? I only hope so.

Hung Tang

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